Obtaining and analyzing samples of fluid from subsurface reservoir formations is often conducted during oil and gas exploration. Such operations are hindered by the harsh subterranean environment specific to oilfields, including high temperature and pressure (HPHT), corrosive fluids, and severely constrained geometry. The difficulty in acquiring and performing measurements on fluidic samples in such an environment are further complicated by use of electronic sensors that typically require power, monitoring and/or telemetry.
Several oil-field related operations, such as fracturing a geological formation, would greatly benefit from the capability of producing a map of the subterranean fracture geometry, and of the fracture evolution in time. Such capability does not currently exist. A similar need exists for a technology which can be used in monitoring and performing fracture analysis of subterranean carbon dioxide sequestration reservoirs.
Measurements of fluid properties and composition far from an oil well are difficult to perform in the oilfield environment. The capability to inject very small sensing devices far into a geological formation by use of a Proppant or similar means of sensor transport, and to be able to determine their position and the precise moment when they perform a measurement or acquire a sample would greatly benefit the industry.
Measurements need to be performed in other types of situations, where the deployment of active sensing systems with on-board electronics and data transmission capabilities may either be impossible due to environmental issues (for example temperatures and pressures that are too high) or may prove to be too expensive to justify economically. Typical examples involve measurements within aquifers, potable water wells, or in a submarine environment. Such an environment may be a lake, or a sea or ocean. Still further environments include where or when there is a lack of power, such as in remote areas of the world.
The capability to perform viscosity measurements on fluid samples is extremely important in a variety of industries: chemical engineering, food industry, oilfield, to name a few. Usually this is accomplished using large laboratory instruments such as capillary viscometers and rheometers, or by using portable lighter weight instruments. In most cases, these instruments are operated using electrical power, and require sample manipulations that are difficult to automate. In some environments such instruments may be impractical due to their size (such as in difficult to reach areas, or within downhole oilfield tools), may be dangerous due to their electrical operation (inside explosive environments such as refinery facilities and tanks, near oil and gas wells), may be incompatible with the shocks or vibrations (within an oil well), or may be simply difficult to adapt. In this case new types of viscosity measurements need to be devised that avoid such inconveniences.
Samples often need to be acquired in explosive atmospheres (ATEX environments) such as inside refinery tanks (to determine the fluid quality and stratification), within refineries or gas plants or other facilities dealing with explosive environments. In such situations the sampling equipment should not pose a risk of generating an explosion, as would be the case if an electrical spark were created. All-mechanical systems that are ATEX-certified are currently used in the industry to perform this type of sampling.
Furthermore, samples may need to be acquired from fluids that are at high pressure, such as in a chemical factory, a refinery, inside an oil well, or at high depth within the ocean. When pressure is lowered, such samples may change (or degrade) by undergoing a thermodynamic phase transition leading to phase separation (i.e. gas may separate from oil, or asphaltenes may precipitate from heavy oil), in a possibly irreversible manner. Sample containers in this case may need to be filled slowly, at controlled inflow into the sample vial or chamber, in order to preserve the thermodynamic equilibrium and prevent, for example, a pressure shock that may lead to phase separation or other irreversible changes in the sample constituency. Such samples may also need to be maintained at high-pressure conditions subsequent to sample acquisition (for example during sample tool retrieval, or during transportation to a remote laboratory), to prevent sample degradation and maintain the sample characteristics unchanged.
Additionally, samples are often required in environments that pose objective risks and dangers, or that are physically remote, or where frequent sampling using manual devices may prove impractical: sites of nuclear disasters, military battlegrounds, biohazard or chemical hazard areas, terrorist attack sites, remote natural resources such as rivers and lakes, coastal waters and other offshore locations, deep water and sub-sea environments. In such cases, robotic equipment may need to be deployed, and the capability to take and analyze such samples may provide important information that cannot be acquired using the on-board in-line sensors present on such equipment. Such equipment may consist of autonomous or remotely-operated vehicles or robots; remotely-operated underwater vehicles; autonomous underwater vehicles such as buoyancy-driven gliders and wave gliders; airborne or ground drones; other type of robotic equipment.
Samples often need to be acquired and analyzed to detect trace levels of certain contaminants that may be too dilute to enable direct detection. Sample pre-concentration may be required in such cases, by methods such as filtration using mechanical filters, polymeric filters, fiber glass filters, affinity columns, solid phase extraction columns, gas chromatography pre-concentration tubes and columns, or other types of material showing particular affinity for the contaminant, and possibly included in porous or packed form. Particular care needs to be taken when acquiring such samples to prevent scavenging of the sample by, or its adsorption to, the materials of the sampling vial or chamber, or of the transport tubes. The filter material may need to be backflushed, often with a different solution, to remove filter cake buildup and to generate a pre-concentrated sample that may need to be stored into a separate vial or container for transport, storage, or for further manipulation and/or analysis. Alternatively, the filter itself may be retrieved and analyzed, after applying an optional extraction protocole, using laboratory equipment such as gas chromatography, high precision liquid chromatography (HPLC), mass spectroscopy, gamma ray spectroscopy, or other analytical chemistry, biochemical, biological, or nuclear equipment, and possibly after solvent or thermal desorption.
Often there is a need to perform a chemical or biochemical reaction on the acquired sample, by bringing it in contact with a known quantity of chemical or biochemical reagent that will lead to a property change as a consequence of the reaction. The chemical or biochemical reagent may be present as a liquid, solid, powder, gel, gas, emulsion or foam, and it may be attached to, or immobilized on, a solid substrate such as the walls of a vial, a strip of metal, tissue, plastic, paper (as is the case of colorimetric test strips). The reagent may be lyophilized. Often, the (bio)chemical reaction results in color change, which can be detected optically by spectrophotometric absorbance or by colorimetry. Other times direct fluorescence of the sample, or the presence of a fluorescent byproduct, can be detected by fluorescence measurements. Many other properties of the sample may be measured such as (without limitation) optical absorbance, chemiluminescence, color, turbidity, fluorescence intensity, index of refraction, conductivity, density, viscosity. In some cases the usage of a microplate with multiple wells may be necessary to prepare a sample and perform measurements on it.
Certain chemical or biochemical sample preparation protocols may require more complex sample manipulations, such as reaction with a first reagent, waiting for an incubation or reaction time, and then bringing the sample in contact with a second reagent. This sequence may need to be repeated several times.
For pollution monitoring, often samples are not acquired instantaneously but rather over longer periods of time. The rate of sample intake may be proportional to flow velocity in the body of water being sampled. This technique provides “integrated” water samples, which allow in some circumstances to determine the average pollution of the body of water over a period of time, rather than instantaneous pollution.
In certain applications, the moment when a sample needs to be acquired may not be known in advance, so that a pre-programmed sampling sequence may not be appropriate. In this case, individual control of the moment when each sample is performed may be required. For example, samples may need to be acquired in the aftermath of an unforeseen accident, or as directed by an external signal.
In some cases, there may be a need to acquire a larger number of samples than the capabilities of a single sampling device. In this case, multiple sampling devices may need to be used in a “daisy chain configuration”, in such a way that once a device acquires its maximum number of samples, it automatically triggers the next device that will take over the sampling tasks. Using this approach, the total number of samples that can be acquired is not limited by the capabilities of an individual device.
Often there is a need for injecting, or liberating, small particles or small amounts of chemicals at predefined times into a remote environment, or into an environment which is difficult to access. Such small particles or chemicals may be used as tracers, may participate in chemical reactions, or may be used as pharmaceuticals. Exemplary environments where such particles, chemicals, or pharmaceuticals may be injected include without limitation oil and water reservoirs, pre-existing or induced fractures within such reservoirs or within other geological formations, oil, water and/or gas wells, water bodies such as lakes, rivers and oceans, or a human body.
Monitoring of hazardous waste disposal reservoirs and of adjacent aquifers for contamination mapping and leaching is also a very important domain, where the need for miniaturized and economical sensing solutions is prominent.